Following error above 700 RPM

[Perryg114]

I am trying to interface a sure servo servo motor to Labview and it has been a royal pain. I have finally got it to sorta work. I can control the drive but if I try to go above about 700 RPM the drive drops out and I get a following error. This happens in MAX and it Labview programs. It also happens on two different machines one with Labview 7.1 and the other with Labview 2009. I am using a PCI-7344 card with a UMI-7764 breakout box. The encoder resolution on the servo drive is set to 10,000 pulses per rev or 2500 lines. I am thinking that MAX can't keep track at that resolution and I am going to try to reduce the resolution and see if that helps. This does not seem to be related to acceleration but velocity. Above 700 RPM is seems that MAX can't read the encoder and it drops out of closed loop control which could be very bad. I am trying to do this is velocity mode. I read another post where someone was having following errors and there was something wrong with his UMI-7774 interface. I may have to go to torque mode but I have not tried that yet. I have done all this with Pacific Scientific Servos and have never had these issues. I have another UMI-7764 box I can try if all else fails.

Perry

[Perryg114]

Ok well I lowered the encoder resolution and I am still having problems. There is something about the encoder communication that is flakey. Sometimes I can't get the motor to initialize at all. This is worse in Labview 2009. I guess I am going to change out the UMI-7764 box and see if that helps.

Perry

[Perryg114]

Not sure if anyone is out there. I have swapped all components around and the problem still exists. I am getting bad communication with the encoders it appears. The problems goes away when I use another brand servo motor and drive. It looks like a hardware problem. I guess I am going to have to put a scope on the encoder and see what I get.

Perry

[Greg-H]

Hi,

Perry I know you and I also have a service request open regarding this issue.

Anyone else who is having a trouble with following errors, take a look at this article:

http://digital.ni.com/public.nsf/allkb/899AE29CB4E3578B8625709D0070A725?OpenDocument

Regards,

Greg H. 

[Perryg114]

I have addressed all these issues mentioned in the article. I think the problem lies in the signals coming from the drive controller. For some reason the NI hardware is not able to reliably read the encoder signals at higher RPM. Lowering Encoder resolution does not fix the problem. So it is not a problem with NI not sampling fast enough. I have an older system that works fine under the same conditions.

Perry

[Perryg114]

I found the problem. When I first hooked up the system, I noticed that it was turning in the wrong direction in response to voltage inputs. Instead of changing the default direction in the drive controller I just swaped the polarity of the analog inputs. The was driving the ground and when the voltage got high enough the encoder voltage was swamped by the analog input voltage. When I put the wires back the way they should be and changed the direction in the drive controller, my following error problems went away.

Perry